Non Destructive Testing for the conservation of cultural and artistic heritage

Introduction

The use of NDT, widely developed in sectors such as the aerospace, energy or naval industry, has recently been adapted to the field of historical heritage, becoming a transversal axis for archaeologists, conservators, engineers and restorers. It takes advantage of technology and its scientific advances to not only explore, but also helps us to learn more about the elements used for a work of art from centuries ago that still maintains its roots in the composition and form that was given to it at the time.

The preservation of cultural and artistic heritage represents one of the most complex challenges of the 21st century, in a context where the risks of structural deterioration, environmental contamination and institutional neglect threaten the integrity of thousands of tangible assets around the world on a daily basis. From bronze sculptures to colonial architectural structures, the need for effective methods that protect without altering has become imperative.

But how can we preserve such heritage monuments without them undergoing structural changes and modifications to their original manufacture? In this scenario, Non-Destructive Testing (NDT) emerges as a crucial scientific tool, allowing the evaluation, diagnosis and monitoring of the condition of heritage works without compromising their stability and authenticity.

Techniques such as radiography, infrared thermography, XRF spectroscopy, ultrasound or 3D scanners have demonstrated their ability to detect internal cracks, corrosion processes, hidden pictorial layers or thermal alterations without direct intervention on the analyzed asset¹. To this end, the real impact of these technologies will be analyzed with documentary support, successful cases, and comparative investment statistics by country.

Science at the service of art and memory

Each country, each with its cultural legacy, has symbols that can identify a city, such as, for example, the Eiffel Tower, the Statue of Liberty, the Tower of Pisa, the Wall of China, the Taj Mahal, etc. States and governments have understood that their preservation lies in the periodic maintenance that must be applied to these monuments in order to continue using both their image and their usefulness for tourism and culture in general.

Non-destructive testing (NDT), also known as Non-Destructive Testing (NDT), comprises a set of scientific techniques used to examine materials, structures or works without altering their original form, function or composition² .Their use in the conservation of cultural heritage has spread during the last decades thanks to advances in spectroscopy, digital imaging, thermal sensors and multispectral analysis.

Digital radiography, for example, makes it possible to visualize internal fractures in sculptures and archaeological objects, detect previous repairs or identify hidden assemblages. Similarly, infrared thermography, a technique that measures the thermal gradient of a surface, has been successfully applied to locate areas of detachment or moisture under pictorial layers without the need for physical contact³.

In the material characterization field, XRF (X-ray fluorescence) spectroscopy stands out for its ability to identify chemical elements present in paintings, metals or ceramics, helping to determine the authenticity and provenance of the works. It is a key tool in the conservation of bronze sculptures, as it allows monitoring their state of corrosion without the need to take destructive samples⁴.

“In ethical terms, the use of NDT responds to the principle of minimum intervention, a fundamental axis in the contemporary conservation of historical heritage, which favors respect for the material, functional and symbolic authenticity of the cultural property”⁵.

Applications and evolution of NDT in cultural heritage

Success stories and advances in Latin America and Europe

It should be recognized that the use of NDT in the heritage field has been progressive and, in many cases, experimental. The interest in the recovery of works and monuments is a responsible statement of their importance.

But it is from the 1990s onwards that European institutions such as the CNA (Centro Nacional de Aceleradores, Spain) began to apply techniques such as neutron analysis, portable XRF and 3D laser scanners in large format works⁶. In parallel, projects such as the Inception Project of the European Union promoted the use of HBIM (Heritage Building Information Modeling) for the three-dimensional digital recording of built heritage, integrating inspection, structure and composition data in a unified model.

In Latin America, the development of NDT has mainly taken place in university spaces and research institutions. Brazil, for example, has pioneered integrated 3D scanning, thermography, ultrasound and georadar testing in historic buildings such as the Independence Monument or the Seminario Presbiteriano do Sul, as part of agreements between Mackenzie University and European universities².

Mexico, for its part, has made applications in archaeological heritage in sites such as Teotihuacán and Monte Albán, with the participation of INAH and the use of infrared thermography technology to identify subway chambers and humidity levels in pyramidal structures⁸.

An outstanding example is the use of combined NDT on colonial religious sculptures in Quito, Ecuador, where XRF spectroscopy and digital radiography allowed the identification of original pigments and internal fractures without affecting the polychrome wood support⁹.

Undoubtedly, the use of NDT has been applied in emblematic works that are part of the heritage of humanity. We see how in Europe, the concern is most notable, especially when portable XRF has been used to analyze Michelangelo’s frescoes in the Sistine Chapel without extracting samples (Giorgi et al., 2010). Also when scanning in Latin America, thermography and ultrasound have been key in the conservation of the Independence Monument in São Paulo².

Another successful case has been the restoration of the Alhambra in Granada, which has used infrared thermography to identify areas of plaster detachment under decorative layers. All these techniques have allowed non-invasive and documented interventions³.

This interdisciplinary approach has been key to the protection of world heritage sites, since it allows for safer, scientifically justified and documented interventions, integrating conservation, art history and structural engineering.

NDT in cultural heritage

Technology at the service of art will always leave questions and opinions. Many of them associated with what some consider an unnecessary expenditure of financial resources that are allocated to art instead of more immediate social priorities. However, there are those who support these executive decisions, but also question how the various testing methods and techniques for inspection and maintenance of an unconventional asset can be successfully applied. And let’s look at some of them:

How are radiography and thermography used in art?

Digital radiography has been used in the inspection of sculptures, paintings and architectural elements to visualize internal structures, evaluate hidden repairs and detect areas of fracture or added materials. In pictorial works.

Infrared thermography has been applied to identify delaminations, humidity, infiltrations, and hidden cracks, especially in sculptures, murals and large format frescoes. In Latin America, its use has been extended in colonial facades and religious monuments where invasive methods are ruled out³.

Why apply NDT in cultural heritage?

The main reason is the principle of no direct intervention. Applying NDT makes it possible to analyze works without altering their physical integrity, which is vital in assets of high historical value, fragile or unique. It also reduces costs and time, improves diagnostics and generates valuable visual documentation for future restoration¹⁰. In archaeological contexts, NDT helps to map buried structures without excavation, allowing in situ preservation strategies.

Do NDTs replace traditional assessment in restoration?

No. They are complementary. While they provide accurate and objective information, NDTs do not replace the work of the conservator or the art-historical analysis. Rather, they enrich the material understanding of the work, guide restoration decisions and optimize the process. Integrating NDT data with historical documentation, iconography studies, and style analysis is the most rigorous approach to cultural heritage conservation¹¹.

Can these techniques be applied to pictorial works?

Yes, and with excellent results. In mural and easel painting, thermography, XRF, infrared reflectography, and UV fluorescence are used to identify pigments, evaluate craquelures, altered areas or repainting. For example, XRF has made it possible to determine the chemical composition of metallic pigments in Renaissance paintings without extracting samples, which is crucial for non-transportable and non-removable works¹.

The study and restoration of one of the most emblematic and delicate works such as The Last Supper deserves a special mention, which began its recovery process in 1977 with the restorer Pinin Brambilla, who in 1999 completed her work, but not without thanking her for the technology used, such as multispectral reflectography in the range of 800 to 1900 nm.

This technology made it possible to examine the underlying layers and better understand Leonardo’s original technique without physically intervening in the work; and to Terahertz Measurements (THz) with FMCW (Frequency-Modulated Continuous Wave) and TDS (Time-Domain Spectroscopy) techniques, which were applied to perform structural studies of the mural painting. This helped restorers detect areas of pigment loss or hidden structural damage and plan precise and minimally invasive interventions to preserve the integrity of the work.

International investments and public policies in patrimonial NDT

The growing use of NDT in cultural heritage is linked to heritage digitization policies, technical cooperation and preservation programs financed by the State. The following is a summary of public investment in NDT technologies for heritage conservation (estimated 2023, in millions of USD):

Italy, France and the United States lead the investment, with solid programs for 3D documentation, spectroscopy and structural monitoring in historical heritage. Spain stands out for its use of scanners in Islamic and Romanesque architecture. In Latin America, Brazil and Mexico concentrate the main initiatives, linked to universities and research centers².

These investments not only seek to preserve the cultural legacy, but also to promote tourism, national identity and scientific-technical development. Projects such as the Inception Project in Europe or the CTPC-ABENDI in Brazil demonstrate how the integration of NDT in public policies generates long-term cultural, economic and academic benefits.

Featured applications and case studies

Globally, non-destructive testing has been applied to emblematic works with successful results. In Europe, for example, portable XRF has been used to analyze pigments in Michelangelo’s frescoes in the Sistine Chapel, without the need for sample extraction⁴. Infrared thermography has been key in the restoration of the Alhambra in Granada, identifying areas with plaster detachment under decorative layers.

In Latin America, the use of thermography, ultrasound, borescopy and 3D scanners has been pioneered in Brazil, where cases such as the Independence Monument in São Paulo have been recorded. In that project, a Leica C10 laser scanner with centimeter resolution was used to create a 3D database with both diagnostic and educational applications².

In Mexico, the National Institute of Anthropology and History (INAH) has employed NDT technologies in archaeological zones such as Monte Albán and Teotihuacán, revealing hidden chambers and thermal anomalies without the need for excavation. These studies have made it possible to preserve fragile structures in situ with minimal intervention, respecting their original context⁸.

In sculptural works, the case of the Statue of Liberty in the United States has been referential: although it is not made of bronze but of copper, its maintenance has required specialized NDT to prevent galvanic corrosion between the coating and its internal iron structure¹².

Technical and ethical challenges

Although non-destructive testing has opened up a universe of possibilities in heritage conservation, the truth is that not everything is as simple as it seems. There are stones in the way. One of the most debated -and rightly so- is the famous principle of reversibility. That is, any intervention should be able to be undone without leaving any scar on the work. But that, in practice, sometimes becomes a delicate balancing act. There are coatings that promise to protect and end up slowly altering the piece, as if the remedy were worse than the disease.

On the more technical side, the picture is also challenging. Good intentions are not enough: much of the equipment needed to apply these techniques – such as portable spectroscopy or high-end thermal cameras – is expensive, requires specialized training and requires complex software to interpret the data. And that, in countries with limited resources, can make these technologies seem like a distant promise rather than a real tool.

In addition, there is not yet a common roadmap. Many of the current uses of NDT in heritage are experimental or isolated. There is a lack of clear protocols, systematization, even basic agreements between institutions. Without a shared vision, it is difficult to compare results or make long-term sustainable decisions.

Therefore, more than just talking about technology, we need to talk about ethics, management and collaboration. Because heritage is not only matter: it is history, identity, living memory. And every effort to preserve it must start from that deep respect for what it means.

Conclusions

Non-destructive testing has been, in many ways, a quiet revolution. They do not make noise, they do not alter what they touch, but they reveal everything. That ability to look inside without hurting, to understand without destroying, has made them fundamental allies in the mission to protect our cultural legacy.

And we are not just talking about technology: we are talking about the possibility of rescuing the essence of a sculpture corroded by time, of discovering the original traces under a layer of paint added centuries later, of seeing the invisible. From XRF spectroscopy to infrared thermography, from 3D scanners to infrared reflectography, these tools have been applied in all kinds of contexts – in colonial churches, Renaissance frescoes, archaeological ruins – with results that seemed impossible before.

But much remains to be done. The challenge lies not only in creating more precise technologies. It lies in making them accessible, training the professionals who will use them, creating international cooperation networks and, above all, establishing regulatory frameworks that promote their adoption without losing sight of ethics and sustainability.

Because the future of heritage is not only played in laboratories. It is built in that alliance between art and science, between past and present. And in that connection, non-destructive testing has something beautiful to offer: the possibility of understanding our past without breaking it, of sustaining it in time, and of transmitting it – intact and understandable – to those who have not yet been born.

References

1. Baglioni, P., Carretti, E., & Chelazzi, D. (2015). Nanomaterials in art conservation. Nature Nanotechnology, 10(4), 287–290. https://doi.org/10.1038/nnano.2015.38 
2. Caldana, V. L., Rolim, M. S., & Michelin, G. A. (2020). Tecnologias para levantamento e ensaios não destrutivos: Ações de cooperação técnica e políticas públicas como perspectivas para a preservação do patrimônio. Gestão & Tecnologia de Projetos, 15(1), 191–213.
3. Rolim, M. S., Michelin, G. A., & Caldana, V. L. (2021). O uso da termografia infravermelha em inspeções não destrutivas no patrimônio histórico. Universidade Presbiteriana Mackenzie.
4. Giorgi, R., Baglioni, M., Berti, D., & Baglioni, P. (2010). New methodologies for the conservation of cultural heritage: Micellar solutions, microemulsions, and hydroxide nanoparticles. Accounts of Chemical Research, 43(6), 695–704. https://doi.org/10.1021/ar900147c 
5. Muñoz Viñas, S. (2005). Contemporary theory of conservation. Routledge.
6. Casiello, A. (2011). Il rilevamento dell’architettura: Tecniche e strumenti per il rilievo architettonico. Firenze: Nardini.
7. Patrucco, G., Gómez, A., Adineh, A., Rahrig, M., & Lerma, J. L. (2022). 3D data fusion for historical analyses of heritage buildings using thermal images: The Palacio de Colomina as a case study. Remote Sensing, 14(22), 5699. https://doi.org/10.3390/rs14225699
8. Rodríguez, M. A., & López, D. (2018). La termografía infrarroja en el diagnóstico de estructuras patrimoniales: Aplicaciones en zonas arqueológicas mexicanas. Revista Arqueología y Ciencia, 12(2), 58–71
9. Fernández, R., & Vázquez, J. (2020). Aplicaciones de la espectroscopía XRF en la conservación de esculturas policromadas en Quito. Revista de Conservación Patrimonial, 18(3), 23–37.
10. Petit, S. (2025). Preservando el pasado con recubrimientos modernos. https://inspenet.com/articulo/recubrimientos-modernos-en-esculturas/ 
11. Ashley-Smith, J. (2018). The ethics of conservation. Getty Conservation Institute.
12. Corrosionpedia. (2023a). Using modern coatings to restore historical New York landmarks. Corrosionpedia. https://www.corrosionpedia.com/using-modern-coatings-to-restore-historical-new-york-landmarks/2/6607